The invention relates to a method for selecting a cylinder group of an internal combustion engine when changing an engine operational parameter.
Known internal combustion engines generally have first and second cylinder groups that are connected to either straight pipe exhaust systems or Y-pipe exhaust systems. Both types of exhaust systems further utilize catalytic converters to reduce automotive emissions.
Known engine control systems utilize a measurement of exhaust gases from the first and second cylinder groups to maintain a predetermined air/fuel ratio in each of the first and second cylinder groups. Generally, the predetermined air/fuel ratio is stoichiometric. Further, when two state exhaust gas oxygen sensors are utilized, a typical result is a fluctuation, or oscillation, of the exhaust air/fuel ratio about the predetermined air/fuel ratio.
With engines having Y-pipe exhaust systems, known control systems have attempted to maintain a desired phase difference between the first and second air/fuel ratio oscillations in the first and second cylinder groups, respectively, to reduce emissions. In particular, known control systems have attempted to phase shift one of the air/fuel ratio oscillations either in phase or out of phase with the non-shifted air/fuel ratio oscillations.
However, the known control systems and methods have not recognized and/or addressed a problem that phase shifting air/fuel ratio oscillations in one of the first and second cylinder groups may result in catalyst breakthrough in a downstream catalytic converter communicating with the shifted cylinder group. Catalyst breakthrough occurs when a catalytic converter is unable to reduce received HC, CO, and NOx emission gases.
The inventors herein have recognized that when selecting one of two cylinder groups for changing an engine operational parameter, such as a phase of air/fuel ratio oscillations, the cylinder group connected to a catalytic converter more capable of maintaining reduced emissions should be selected. In other words, the cylinder group connected to the catalytic converter less likely to have catalyst breakthrough should be selected for changing the engine operational parameter.
The invention relates to a method for selecting one of first and second cylinder groups of an internal combustion engine. In general, a cylinder group is selected that is most capable of having an engine operational parameter changed therein, without resulting in increased emissions from a downstream catalytic converter.
The method for selecting one of first and second cylinder groups of an internal combustion engine may be implemented in an engine having first and second cylinder groups coupled with first and second catalytic converters, respectively. The method includes identifying one of the first and second catalytic converters by comparing first and second catalyst parameters associated with the first and second catalytic converters, respectively. Each of the first and second catalyst parameters may include (i) a catalyst volume (ii) an amount of catalyst material, or (iii) a catalyst conversion efficiency. Catalyst parameters (with similar units) are compared to one another to determine whether one of the catalytic converters is less likely to have catalyst breakthrough when modifying an engine operational parameter therein. Finally, the method includes selecting one of the first and second cylinder groups coupled to the identified catalytic converter for changing an engine operational parameter in the selected cylinder group.
The inventive method provides a substantial advantage over known engine control methods. In particular, when an engine operational parameter is to be changed, the method selects the cylinder group (and catalytic converter) that is best capable of maintaining reduced emissions during the adjustment of the engine operational parameter.